Disclosed herein are phase change ink compositions containing quinacridone pigments. More specifically, disclosed herein are phase change inks containing quinacridone pigments along with pigment dispersants and specific synergists.
In general, phase change inks (sometimes referred to as “hot melt inks”) are in the solid phase at ambient temperature, but exist in the liquid phase at the elevated operating temperature of an ink jet printing device. At the jet operating temperature, droplets of liquid ink are ejected from the printing device and, when the ink droplets contact the surface of the recording substrate, either directly or via an intermediate heated transfer belt or drum, they quickly solidify to form a predetermined pattern of solidified ink drops. Phase change inks have also been used in other printing technologies, such as gravure printing, as disclosed in, for example, U.S. Pat. No. 5,496,879 and German Patent Publications DE 4205636AL and DE 4205713AL, the disclosures of each of which are totally incorporated herein by reference.
Phase change inks are desirable for ink jet printers because they remain in a solid phase at room temperature during shipping, long term storage, or the like. In addition, the problems associated with nozzle clogging as a result of ink evaporation with liquid ink jet inks are largely eliminated, thereby improving the reliability of the ink jet printing. Further, in phase change ink jet printers wherein the ink droplets are applied directly onto the final recording substrate (for example, paper, transparency material, or the like), the droplets solidify immediately upon contact with the substrate, so that migration of ink along the printing medium is prevented and dot quality is improved.
Organic pigments disperse with difficulty in non-polar media such as phase change ink carriers. One approach for dispersing pigments is to modify the surface of the pigment by addition of compounds known as synergists. A pigment stabilizer or synergist works by enhancing the attachment of a dispersant onto the pigment particle.
Quinacridone pigments in particular are very difficult to disperse and stabilize in low polarity waxes and resins such as those often used in phase change inks. The use of synergists is almost always needed in conjunction with a pigment dispersant to stabilize pigments of this class in a phase change ink having low polarity waxes and resins as the carrier.